1. Field of the Invention
This invention relates in general to downhole drilling tools, and in particular to swivels for use with downhole drilling motors.
2. Description of the Prior Art
A downhole drilling motor, or mud motor, is a drilling tool which rotates a drill bit in response to drilling mud being circulated down the interior of the drill string and back up the annulus between the drill string and the sides of the drilled hole. Since mud motors make it unnecessary to rotate the drill string, such motors are particularly useful in drilling directional holes.
A downhole drilling motor has a stationary member, which is connected to the drill string, and a rotating member, which connects to the drill bit. The stationary member and the rotating member are separated by radial and thrust bearings, which may be cooled directly by the drilling mud or sealed in lubricant. Either the stationary member or the rotating member may be located radially outward from the other member.
The rotary seals used to seal downhole drilling motors have a longer useful life if the seals are kept lubricated. As lubricant leaks past the seals, new lubricant must be introduced into the lubricant chamber to maintain and replenish the lubricant around the sealed area. Several methods of replenishing the lubricant are known. U.S. Pat. Nos. 4,114,703 (Matson, Jr. et al.); 4,256,189 (Fox et al.); and 4,284,149 (Fox) each show well drilling tools in which the pressure of the drilling fluid moves a piston to force additional lubricant into the lubricant chamber. In each of these tools, the piston is an annular ring and operates within an annular lubricant passage.